The present invention generally relates to an electrophotographic copying machine of a type capable of making copies at different magnifications one at a time and, more particularly, to a lens positioning mechanism for repositioning an objective lens assembly according to the selection of one of the magnifications available in the copying machine.
In most types of electrophotographic copying machines, there is employed an optical apparatus comprising a plurality of mirrors and an objective lens assembly for forming an image of an original to be copied on a photoreceptor. Where the image of the original to be copied is to be formed on the photoreceptor at a magnification, or on a scale, equal to the size of the image of the original, the distance a of the optical path between the original and the objective lens assembly is set to be equal to the distance b of the optical path between the objective lens assembly and the photoreceptor while the mirrors are arranged in such a manner as shown in FIG. 1 of the accompanying drawings to make each of the distances a and b twice the focal length f of the lens assembly. Referring to FIG. 1, rays of light reflected from the original 8 placed on a transparent original support 1, such as a glass plate, are guided towards the objective lens assembly 5 by way of first, second and third mirrors 2, 3 and 4 and, after having passed through the lens assembly 5, towards a photoreceptor drum 7 by way of a fourth mirror 6, thereby casting the image of the original 8 upon the surface of the photoreceptor drum 7. It is well known that, in the case of equal size reproduction, the distance a of the optical path between the original 8 and the lens assembly 5 by way of the mirrors 2 to 4 and that b of the optical path between the lens assembly 5 and the photoreceptor drum 7 by way of the mirror 6 have the following relationship with respect to the focal length f of the lens assembly 5: (1/a)+(1/b)=1/f.
On the other hand, the magnification m is known as expressed by the ratio of the distance b relative to the distance b, namely, m=b/a. Accordingly, where the equal size reproduction is desired to be accomplished, the mirrors 2, 3, 4 and 6 have to be arranged relative to the lens assembly 5 so as to establish the following relationship: a=b=2f.
It is also known that, where a copy is desired to be made at a magnification different from that used during the equal size reproduction, one of the distances a and b has to be adjusted relative to the other of the distances a and b according to the desired magnification and the lens assembly and the mirrors have to be correspondingly repositioned. By way of example, in a copying machine employing the same lens assembly for the reproduction at the different magnifications, the adjustment can be accomplished by repositioning both the lens assembly 5 and the mirror 6. The direction of movement of the lens assembly 5 is, however, to be parallel to the optical axis of such lens assembly 5 in the case where the original to be copied is, irrespective of its size, adapted to be centered on the original support and the photoreceptor drum is correspondingly adapted to receive the image of the original at its center. That is, since the original laid on the original support and a copying paper on which the image of the original is to be reproduced are all centered with the optical axis of the lens assembly 5, the movement of the lens assembly 5 in a direction axially of the optical axis thereof to a position different from that that has been required during the equal size reproduction results in a proper reproduction of the image of the original on the copying paper at an increased or reduced magnification. Thus, if the lens assembly 5 is moved axially of the optical axis to a position shown by the chain line in FIG. 1, the fourth mirror 6 has to be moved in the same direction to a position shown by the corresponding chain line in FIG. 1 in order for the machine to be set at a magnification determined by the ratio of the distance b relative to the distance a, that is, b/a. At the same time, the fourth mirror 6 is also rotated in a direction shown by the arrow because the movement of the mirror 6 when kept in parallel relation to the original position may result in the reflection of the optical image at a position displaced from the position P on the photoreceptor drum. Thus, by adjusting the respective positions of the lens assembly and the mirror 6, the copying operation can be accomplished at a magnification defined by the ratio of the distance b relative to the distance a. In such a copying machine, the copying paper is always transferred to the photoreceptor drum 7 while having been aligned with the center thereof.
On the other hand, in the alignment method wherein the original is adapted to be laid on the original support with its one side held constantly in abutting relation to one edge of the original support, the mere adjustment of the lens assembly 5 in a direction parallel to the optical axis of the latter does not result in the formation of the image of the original correctly on the photoreceptor drum 7. This is because the side of the original on the original support held against the edge of the latter will not align with a corresponding side edge of a copying paper. Therefore, in such a method, the lens assembly has to be also moved in a direction perpendicular to the plane of the drawing of FIG. 1. This is essentially required for a particular area of the photoreceptor drum 7, where the image of the original is formed, to be exactly aligned with the copying paper having its side edge regulated.
This will now be discussed in detail with particular reference to FIG. 2. Referring to FIG. 2, the original 8 is shown as placed on the original support 1 with its one side 8-1 held against a reference edge of the original support 1. The photoreceptor drum 7 is schematically shown in the form of a photoreceptor surface. The arrow marking shown beside the original 8 in FIG. 2 represents the direction of movement of the original support and, hence, the original 8 and the arrow marking shown beside the photoreceptor 7 represents the direction of rotation of the photoreceptor 7. As shown, the image of the side 8-1 of the original which has been projected through an optical apparatus 9, including the mirrors 2 to 4 and 6 of the lens assembly 5, so as to align with a reference edge 7-1 of the photoreceptor 7 during the equal size reproduction, will not be formed on the photoreceptor 7 in alignment with the reference edge 7-1 if the lens assembly 5 is merely repositioned in a direction parallel to the optical axis h thereof during an attempt to make a copy at a reduced magnification. Accordingly, in order to keep the side 8-1 of the original aligned with the reference edge 7-1 of the photoreceptor 7 irrespective of the magnification, the lens assembly 5 has to be adjusted in a diagonal direction, as shown by the arrow.
According to the above described method, where the number of magnifications available is two, for example, an equal size reproduction (the ration b/a being 1) and a reduced magnification (the ration b/a being smaller than 1), the linear adjustment of the lens assembly 5 in the diagonal direction effectively results in the formation of the image of the original on the photoreceptor 7 with the side 8-1 aligned with the reference edge 7-1. However, if it were three or more, at least one or more of the optical image can no longer be aligned exactly with the reference edge of the photoreceptor. In other words, the optical image will be merely formed adjacent the reference edge of the photoreceptor.
The foregoing description applies where, while the lens assembly 5 has a fixed focal length f, change in magnification is accomplished by repositioning the lens assembly 5 together with a corresponding repositioning of the mirror 6. However, the mirror 6 may not be adjusted if an auxiliary lens assembly is employed to change the focal length f of the lens assembly and the sum of the distances a and b is kept at a constant value. It is to be noted that a similar description applies where, instead of the use of the auxiliary lens assembly, the lens assembly 5 is employed in the form of a zoom lens assembly.
In any event, U.S. Pat. No. 3,614,222, patented Oct. 19, 1971, to Gerald Post et al., discloses a copying machine in which the transparent original support is adapted to support originals thereon one at a time in a manner with two adjacent sides of each original held always in abutting relation to two right-angled edges of the original support no matter what magnification the image of each original is reproduced at. This patent also discloses a mechanism operable, when the magnification is changed, to drive the lens assembly in a direction close to or away from the photoreceptor and, simultaneously, in a direction perpendicular to the optical axis of the lens assembly. More specifically, in the copying machine disclosed in the above mentioned patent, when the magnification is to be changed from, for example, a 1:1 ratio to a 1:0.7 ratio, the lens assembly which has been held at a certain position during the equal size reproduction is repositioned to a position closer to the photoreceptor drum than at such certain position and offset laterally from such certain position in a direction generally perpendicular to the optical axis thereof. For this purpose, according to the 222 patent, a carriage for the support of the lens assembly is, while the lens assembly is rigidly mounted thereon with its optical axis extending at right angles to a plane parallel to the photoreceptor surface, adapted to be driven in a direction close to and away from the photoreceptor at a preset angle relative to the optical axis each time the magnification is changed.